net: ipv6: IEEE 802.15.4 short address fix

If IPv6 address is generated from IEEE 802.15.4 short address,
then the Universal/Local bit must be set to 0.

See RFC 6282 chapter 3.2.2 for details.

Change-Id: Ied38f40e807bdcd792570b331f6b99a6fcc7db1b
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>